The present invention generally relates to electric motors. More particularly, this invention relates to electric motors of types that are adapted to drive windshield wipers and incorporate a dynamic park capability.
The motor vehicle industry utilizes electric motors to drive windshield wipers. In general, a windshield wiper system having a dynamic park function comprises a motor, a rotary-to-linear motion converter mechanism, windshield wipers, a switch for controlling the motor, and a park disk. An exemplary 24 volt direct current (DC) windshield wiper motor 10 as known in the art is represented in FIG. 1.
As conventional in the art, the motor 10 may be controlled, for example, with a manual selector switch 17 (FIGS. 10-12), to be operable in any one of three possible modes of operation: park, high speed, and low speed. The motor 10 incorporates a park disk 12 for what is known and referred to as dynamic parking which is a process of returning the windshield wipers to their original starting or ‘park’ positions when the motor 10 is turned off with the switch 17. The park disk 12 is rotatably mounted within a gear head 13, rotates as a result of engaging a worm gear 15 driven by a rotor (not shown) within an electric motor housing 11 of the motor 10, and drives a rotary-to-linear motion converter mechanism functionally coupled to a windshield wiper (not shown). The park disk 12 is a circular disk-shaped component that includes a ground tab 14, park section 16, and battery positive section 18. FIG. 2 represents an interior portion of a gear housing plate 20 that is configured to be assembled to the gear head 13 for interaction with the park disk 12 of FIG. 1. The gear housing plate 20 has ground, park, and battery positive contacts 22, 24 and 26, respectively, which interact with the ground tab 14, park section 16, and battery positive section 18, respectively, of the park disk 12 as the park disk 12 rotates. FIG. 3A represents a diagram of the park disk 12 as assembled with three armatures corresponding to the ground, park, and battery positive contacts 22, 24 and 26. FIG. 10 is a wiring diagram representing a system and method of wiring the park disk 12 to the switch 17 and a battery 13. As represented, a positive terminal (‘+’) of the battery 13 is connected to the switch 17 and a negative terminal (‘−’) of the battery 13 is connected directly to a contact 21 on the motor 10. The high input wire 52, low input wire 50, and park wire 54 connect the switch 17 to contacts 21 on the motor 10. The switch 17 is connected by a battery positive wire 52 to the battery positive contact 26 at the park disk 12. In FIG. 10, the switch 17 is set to the park position (‘off’) thereby electrically connecting the park wire 54 to the low input wire 50. In the figures, the position of the switch 17 is depicted by a solid arrow. The motor 10 is represented as being turned off and the park disk 12 is located in the park position.
During operation, when the manual selector switch 17 (motor switch) is set to a low or high position (‘low’ or ‘high’), the motor 10 operates in low or high speed mode, respectively. Operation of the motor 10 consequently rotates the park disk 12 and, through the rotary-to-linear motion converter mechanism, moves the windshield wipers back and forth across the windshield both at low or high speed depending on the mode of operation of the motor 10. While the motor 10 is running in low or high speed modes, the park disk 12 continuously rotates, with each full rotation corresponding to one complete swipe (across the windshield and back to the park position) of the windshield wipers.
FIG. 11 represents the wiring diagram of FIG. 10 when the switch 17 is set to the low position (‘low’) thereby connecting the low input wire 50 to the positive terminal on the battery 13, and the motor 10 is operating in low speed mode. Current flows from a positive terminal on a battery 13 to the switch 17, through the switch 17 to a low input wire 50, through the low input wire 50 to the motor 10 (via contact 21), through the motor 10 to a battery negative wire 56 (via contact 21), and through the battery negative wire 56 to the negative terminal on the battery 13 (or ground). During this time, the high input wire 52 and the park wire 54 are open at the switch. The park disk 12 is represented as being in an exemplary transient operating position. It should be understood that the system operates in substantially the same manner when in high speed mode rather than low speed mode. When the switch 17 is set to the high position (‘high’), the high input wire 52 is connected to the positive terminal on the battery 13, and the low input wire 50 and park wire 54 remain open.
If the switch is moved to the park position (‘off’) while the motor 10 is operating in low or high speed mode, the park disk 12 enters the park mode and continues to rotate, for example, through the transient position shown in FIG. 3A, until it reaches a predetermined park position, represented in FIG. 3B. FIG. 12 represents the wiring diagram of FIG. 11 when the switch is set from the low position (‘low’) to the park position (‘off’) and the motor 10 is operating in park mode. The switch 17 connects the park wire 54 and the low input wire 50 such that current flows from the positive terminal on the battery 13 to the switch 17, through the switch 17 to a battery positive wire 58, through the battery positive wire 58 to the park disk 12 (via the contact 21 and the battery positive contact 26), through the park disk 12 to a park wire 54 (via the park contact 24), through the park wire 54 to the switch 17, through the switch 17 to the low input wire 50, through the low input wire 50 to the motor 10 (via contact 21), through the motor 10 to the battery negative wire 56 (via contact 21), and through the battery negative wire 56 to the negative terminal on the battery 13 (or ground). During this time, the low input wire 50 and the high input wire 52 are not directly connected to the positive terminal of the battery 13 within the switch 17, rather power is provided through the park wire 54. If the park disk 12 is in a transient operating position, as represented in FIG. 12, the motor will continue to operate at low speed and until the park disk rotates to the park position, represented in FIGS. 3B and 10.
As represented in FIG. 3B, the park position of the motor 10 is reached when the battery positive contact 26 is suspended over an opening 19 in the park disk 12 and therefore is not electrically connected to the battery positive section 18, the park contact 24 is electrically connected to the park section 16, and the ground contact 22 is electrically connected to the ground tab 14. Once the park disk 12 reaches the park position, the circuit represented in FIG. 12 is opened as a result of the battery positive contact 26 no longer being in contact with the battery positive section 18 and the motor 10 functions as a load generator developing a torque that rapidly stops the motor 10 and thereby stops the windshield wipers in their park position. The dynamic park function ensures that the windshield wipers will always return to their park position regardless of their current position when the switch 17 is turned to ‘off.’
In normal operation of the motor 10 in either high or low speed modes, the park disk 12 continuously rotates and makes contact to both +24 volts (i.e., battery positive contact 26 electrically connected battery positive section 18) and ground (i.e., ground contact 22 electrically connected to ground tab 14) once during each revolution of the park disk 12 thereby sequentially creating a negative pulse and a positive pulse of conducted and radiated electromagnetic emissions. On dynamic park motors such as the windshield wiper motor 10 of FIG. 1, these pulses occur when the voltage goes from +24 volts to ground (0 volts) and then back to +24 volts. For example, FIG. 4A represents a measurement of pulses taken from a conventional dynamic park motor, such as the motor 10 of FIG. 1, as the park disk 12 rotates. These pulses may travel through wires exiting the motor 10, for example, high input wire 52, low input wire 50, park wire 54, battery positive wire 58, and battery negative wire 56, and radiate therefrom causing electro-magnetic interference (EMI) during each revolution of the park disk 12.
Increasingly, electronic devices are installed in or used around motor vehicles which are sensitive to the EMI generated by electric motors. In certain cases, EMI can pose a security risk. For example, the EMI generated by the windshield wiper motor 10 of FIG. 1 can be detected and traced to a military vehicle in which the motor 10 is installed, indicated by a repeating signal on radar which reveals the location and direction of the vehicle. Such military vehicles must meet strict government EMI control regulations, such as U.S. military standard MIL-STD-461F. Consequently, there is a need for systems and methods suitable for reducing or eliminating this pulse of electromagnetic emissions.